000 AXNT20 KNHC 201750 TWDAT TROPICAL WEATHER DISCUSSION NWS TPC/NATIONAL HURRICANE CENTER MIAMI FL 205 PM EDT THU AUG 20 2009 TROPICAL WEATHER DISCUSSION FOR NORTH AMERICA...CENTRAL AMERICA...GULF OF MEXICO...CARIBBEAN SEA...NORTHERN SECTIONS OF SOUTH AMERICA...AND ATLANTIC OCEAN TO THE AFRICAN COAST FROM THE EQUATOR TO 32N. THE FOLLOWING INFORMATION IS BASED ON SATELLITE IMAGERY...METEOROLOGICAL ANALYSIS...WEATHER OBSERVATIONS...AND RADAR. BASED ON 1200 UTC SURFACE ANALYSIS AND SATELLITE IMAGERY THROUGH 1715 UTC. ...SPECIAL FEATURES... LARGE HURRICANE BILL IS CENTERED NEAR 22.6N 61.7W OR ABOUT 330 NM...610 KM...NORTH OF THE LEEWARD ISLANDS MOVING NW OR 305 DEG AT 16 KT. THE LATEST MINIMUM CENTRAL PRESSURE REPORTED BY A NOAA P-3 HURRICANE RECONNAISSANCE AIRCRAFT WAS 951 MB. MAXIMUM SUSTAINED WIND SPEED IS 105 KT WITH GUSTS TO 130 KT. SEE THE LATEST FORECAST/ADVISORY UNDER AWIPS/WMO HEADERS TCMAT3/WTNT23 KNHC FOR MORE DETAILS. ALTHOUGH BILL WEAKENED SLIGHTLY TO A CATEGORY 3 STORM TODAY...REINTENSIFICATION IS FORECAST DUE TO ITS PASSING OVER THE WARMER WATERS AND LIGHTER WIND SHEAR. HURRICANE BILL CONTINUES TO DISPLAY A WELL DEFINED EYE WITH NUMEROUS STRONG CONVECTION WITHIN 60 NM NE AND 80 NM SW SEMICIRCLES. SCATTERED TO ISOLATED STRONG CONVECTION IS OBSERVED IN OUTER SPIRAL RAINBANDS. LARGE SWELLS GENERATED BY THIS HURRICANE ARE AFFECTING THE NORTHERN LEEWARD ISLANDS AND SHOULD BEGIN TO AFFECT THE BAHAMAS...BERMUDA...MOST OF THE EASTERN U.S. COAST... AND THE ATLANTIC MARITIMES OF CANADA DURING THE NEXT FEW DAYS. THESE SWELLS WILL LIKELY CAUSE EXTREMELY DANGEROUS SURF AND LIFE-THREATENING RIP CURRENTS. ...TROPICAL WAVES... A TROPICAL WAVE IS ALONG 23W S OF 18N MOVING W AROUND 10 KT. THE WAVE IS EMBEDDED WITHIN AN AREA OF DEEP LAYERED MOISTURE MAXIMUM OBSERVED IN THE TOTAL PRECIPITABLE WATER IMAGERY. AN INVERTED-V LOW LEVEL SIGNATURE IS NOTED ON VIS SATELLITE PICTURES WITH SOME CYCLONIC TURNING NEAR THE INTERSECTION OF THE WAVE WITH THE ITCZ. SCATTERED SHOWERS AND ISOLATED TSTMS ARE WITHIN 160-200 NM EITHER SIDE OF THE WAVE AXIS. THE WAVE WILL CONTINUE TO MOVE ACROSS THE CAPE VERDE ISLANDS THIS AFTERNOON. A TROPICAL WAVE IS ALONG 49W/50W S OF 15N MOVING W 15-20 KT. THE WAVE SHOWS UP WELL IN THE UW-CIMSS TPW WHERE A BULGE OF MOISTURE IS NOTED. ONLY FEW SHOWERS ARE ASSOCIATED WITH THIS FEATURE DUE TO THE PRESENCE OF DRY AIR. THIS WAVE WILL REACH THE TROPICAL N ATLC LATE TONIGHT INTO FRI MORNING. A TROPICAL WAVE IS CURRENTLY MOVING ACROSS THE YUCATAN PENINSULA AND NORTHERN CENTRAL AMERICA. ITS AXIS IS ALONG 88W/89W S OF 21N MOVING W 10-15 KT. THE WAVE IS WELL DEPICTED IN THE MOISTURE PRODUCT...TPW...AND IS EXPECTED TO MOVE ACROSS THE BAY OF CAMPECHE THIS AFTERNOON THROUGH TONIGHT HELPING TO INDUCE SOME SHOWER ACTIVITY. ...THE ITCZ... THE ITCZ AXIS IS CENTERED ALONG 12N16W 9N30W 10N44W 8N56W 10N62W. CLUSTERS OF SCATTERED MODERATE TO ISOLATED STRONG CONVECTION IS FROM 10N TO 13N E OF 20W TO THE COAST OF AFRICA. A BAND OF SCATTERED MODERATE CONVECTION IS ROUGHLY WITHIN 120 NM N OF AXIS BETWEEN 28W AND 45W. ...DISCUSSION... GULF OF MEXICO... BROAD UPPER RIDGE COVERS MOST OF THE GULF REGION EXTENDING FROM CENTRAL MEXICO NEAR 20N100W NNE TO OVER THE LOWER MISSISSIPPI VALLEY TO THE CAROLINAS WHILE A UPPER-LEVEL LOW CONTINUES TO SPIN OVER THE GULF OF HONDURAS. A SHORT-WAVE TROUGH IS OVER SOUTHERN TEXAS. AT THE SURFACE...A RIDGE FROM THE W ATLC CONTINUES TO BUILD ACROSS THE GULF PRODUCING MAINLY LIGHT TO MODERATE SE TO S WINDS. ISOLATED SHOWERS CONTINUE TO DOT THE AREA PARTICULARLY THE E GULF. ALL THESE SHOWERS ARE MOVING NWD UNDER THE PREVAILING WIND FLOW. CARIBBEAN SEA... A QSCAT PASS FROM THIS MORNING SHOWED MODERATE TO STRONG WINDS OF 20 TO 25 KT JUST OFF THE COAST OF COLOMBIA COAST. THE TRADES WILL DECREASE FRI AND INTO THE WEEKEND AS THE ATLC HIGH WEAKENS WITH HURRICANE BILL MOVING N OF THE FORECAST AREA. TYPICAL SHOWERS EMBEDDED IN THE TRADE WIND FLOW ARE SEEN ACROSS THE BASIN. NLY WINDS ON THE WEST SIDE OF HURRICANE BILL ARE PUSHING SOME NARROW LINES OF SHOWERS SWD INTO THE FAR NE CARIBBEAN AS SEEN ON THE SAN JUAN DOPPLER RADAR. THESE SHOWERS ARE IN ASSOCIATION WITH THE CYCLONIC FLOW AROUND BILL. ALOFT...AN UPPER-LEVEL LOW IS OVER THE GULF OF HONDURAS COVERING THE NW CARIBBEAN. ANOTHER UPPER-LEVEL LOW IS OVER HISPANIOLA. IN BETWEEN...AN UPPER RIDGE EXTENDS FROM PANAMA TO THE CAYMAN ISLANDS. UPPER DIFFLUENCE ASSOCIATED WITH THIS FEATURE IS HELPING TO INDUCE SCATTRED SHOWERS AND ISOLATED TSTMS OVER THE SW CARIBBEAN S OF 12N. ATLANTIC OCEAN... ATTENTION REMAINS FOCUSED ON BILL...THE FIRST MAYOR HURRICANE OF THE 2009 ATLANTIC HURRICANE SEASON. SEE SPECIAL FEATURES FOR DETAILS. THE AZORES-BERMUDA HIGH EXTENDS A RIDGE OVER THE CENTRAL AND EASTERN ATLC. BILL IS MOVING AROUND THE PERIPHERY OF THIS HIGH. A WEAK SFC RIDGE ALSO DOMINATES THE SW ATLC AND THE STATE OF FLORIDA. PRES GRADIENT BETWEEN HIGH PRES OVER THE AZORES AND HURRICANE BILL IS PRODUCING A SWATH OF MODERATE TRADE WINDS FROM 12N TO 24N E OF 50W. ALOFT...NARROW UPPER TROUGH ENTERS THE AREA NEAR 32N68W THEN CONTINUES SW TO NEAR THE SE BAHAMAS. AN UPPER LOW IS ALONG THE TROUGH NEAR 27.5N71W GENERATING SOME SHOWER ACTIVITY. THE FLOW EAST OF THE UPPER-LOW IS HIGHLY AMPLIFIED ANTICYCLONICALLY DUE TO THE VERY PRONOUNCED OUTFLOW OF LARGE HURRICANE BILL. AN UPPER-LEVEL RIDGE FROM THE GULF OF MEXICO EXTENDS INTO THE W ATLC W OF 73W. $$ GR